OFDM and OFDMA wireless communication systems under IEEE 802.16 use a network of base stations to communicate with wireless devices (i.e., mobile stations) registered for services in the systems based on the orthogonality of frequencies of multiple subcarriers and can be implemented to achieve a number of technical advantages for wideband wireless communications, such as resistance to multipath fading and interference. Each base station emits and receives radio frequency (RF) signals that convey data to and from the mobile stations. Such an RF signal from a base station includes an overhead load, in addition to the data load (voice and other data), for various communication management functions. Each mobile station processes the information in the overhead load of each received signal prior to processing the data.
Under the current versions of the IEEE 802.16x standards for the OFDM/A systems, every downlink subframe from a base station includes a preamble and a frame control header (FCH) following the preamble as part of the overhead load. The preamble includes information for searching a cell and a cell sector within a cell and for synchronizing a mobile station in both time and frequency with the received downlink signal. The FCH portion of the downlink subframe includes 24 bits with information on the downlink transmission format (e.g., the downlink media access protocol, or DL MAP) and control information for the downlink data reception (e.g., allocation of the subcarriers in the current downlink frame).
Therefore, a receiver, such as a mobile station, first decodes the FCH to determine the position of the DL MAP, decodes the DL MAP of the corresponding position, and then extracts the data. Due to the nature of the information in the FCH, if the reception of FCH fails or the FCH is decoded incorrectly, the following downlink operations on the receiver side cannot be properly executed. Accordingly, proper interpretation of the FCH is important to OFDM and OFDMA system operation.